Memory modules are used for simultaneously actuating a plurality of semiconductor chips, for example DRAMs (dynamic random access memories), which are operated in parallel with one another and, therefore, all receive electrical signals at the same time. To distribute the electrical signals, an electronic printed circuit board is used that has chip contact connections and a connector strip that is used to connect the printed circuit board to a superordinate electronic unit, for example to a mother board. The connector strip may be formed on one or two outer faces of the printed circuit board and has a respective multiplicity of contact connections that are lined up in a first direction along a first edge of the printed circuit board.
Conductor tracks on or in the printed circuit board run between the contacts of the connector strip and the chip contact connections and also further components, such as registers, PLLs (phased-locked loops), etc. Normally, the conductor tracks in today's memory modules are formed on a plurality of planes within a multicomponent electronic printed circuit board. The conductor tracks may respectively run within a conductor plane on the printed circuit board or may run in sections over various conductor track planes that are connected to one another by appropriate electrically conductive contact-hole fillers.
The storage capacity of today's memory modules is increasingly large, since firstly the storage capacity of the semiconductor chips themselves is becoming ever larger and secondly an increasingly large number of semiconductor chips is being mounted on a printed circuit board. In this case, the area of the printed circuit board must not be increased if at all possible or at most slightly.
Many memory modules have electronic printed circuit boards that are fitted with DRAMs or other semiconductor memories of the same type as one another frequently in mirror-image symmetrical form relative to the center of the connector strip and hence in mirror-image symmetrical form relative to the center of the memory module. By way of example, it is possible for nine respective semiconductor chips of the same type to be mounted next to one another between the center of the memory module and a respective second edge of the printed circuit board that runs in a second direction perpendicular to the connector strip. Eight of the semiconductor chips on each half of an outer face of the printed circuit board are used to store the actual storage data, whereas a ninth semiconductor chip is used as an ECC (error correcting code) chip, which prevents storage errors or reading errors by comparing the signals from the remaining eight memory chips.
When, by way of example, nine semiconductor chips of the same type are arranged per half of the outer face of the printed circuit board (for example in each case on both halves of the front of the printed circuit board), the problem is to find an arrangement of memory chips that is compatible with the demand for the most uniform possible signal propagation times to all the semiconductor chips and the most equal possible conductor track lengths. Added to this is the desire to manage as far as possible without any signal drivers along the conductor tracks, as these would take up additional space on the conductor track.